This invention relates to hydraulic emergency shut-down systems (ESD) for actuating closure of valves.
U.S. Pat. No. 6,276,135 issued Aug. 21, 2001, and Canadian application no. 2,266,806 published Sep. 23, 2001, describe a hydraulic control circuit for a hydraulic actuator, including a high-low pilot valve having a sensing port for connection to a flow line. When the sensed pressure from the flow line moves outside of a pre-set operating range, the hydraulic actuator is actuated and flow in the line is stopped. For initiating the operation of the high-low pilot, a time out valve is closed on the hydraulic control circuit to allow manual build up of pressure in the hydraulic control circuit to the operating range. This opens the hydraulic actuator and the high-low pilot maintains pressure on the hydraulic circuit to keep the hydraulic actuator open.
A difficulty occurs with this hydraulic control circuit in that there may be a period in which the time-out valve is closed, but the hydraulic actuator is open, so that there is fluid flow in the flow line, with no way to monitor the pressure in the flow line.
This invention is directed to providing increased safety of operation of a self-contained hydraulic emergency shut down system.
Therefore, according to an aspect of the invention, there is provided a hydraulic control circuit, comprising a control line connected to a device to be controlled by fluid pressure in the control line; a time-out valve on the control line, the time-out valve having a time-out period during which time-out period operation of the time-out valve is delayed after actuation of the time-out valve; a pump connected to the control line for pressurizing the control line with fluid; and an arming valve operated by pressure on an arming line connected to the control line and the arming valve being connected to the time-out valve to reduce the time-out period in response to pressure on the control line.
The hydraulic control circuit has particular utility for use with a flow line and the device to be controlled is a valve on the flow line.
In a further aspect of the invention, the time-out valve includes a restrictor on a fluid return line that regulates the time-out period. The restrictor may comprise plural loops of continuous tubing arranged in plural layers, preferably spirally wound, the tubing having a smaller inner diameter than the fluid return line. In a further aspect of the invention, the arming valve operates a bypass around the restrictor. In a further aspect of the invention, the time-out valve is normally open, and is closed after actuation until expiry of the time-out period.
In addition, this invention provides a novel configuration of bias restrictor for use on a control line on a hydraulic circuit. The restrictor comprises plural loops of continuous tubing arranged in plural layers, preferably spirally wound, the tubing having a smaller inner diameter than the control line.
These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow.